Applicants claim priority under 35 U.S.C. xc2xa7119 of German Application No. 198 33 594.6 filed Jul. 25, 1998. Applicants also claim priority under 35 U.S.C. xc2xa7120 of PCT/DE99/02244 filed Jul. 21, 1999. The international application under PCT article 21(2) was not published in English.
1. Field of the Invention
The invention relates to a procedure for manufacturing a one-piece, profiled, hollow steel camshaft. Profiled denotes that the camshaft is tubular, with a profiled inner jacket surface, which in some extent matches the contours of the cams and bearing areas on the camshaft.
2. The Prior Art
Steel camshafts are known from JP 02 102 302 A, JP 41 67 946 A, JP 12 38 765 A, JP 63 264 248 A for example.
Generic camshafts are suitable and intended for valve trains of internal combustion engines, in which the valves are actuated in particular through roller contact with the camshaft. In these cases, camshafts are required that can withstand Hertzian surface pressures of up to 2,500 MPa during the entire engine service life without any damage to its bearing surfaces. The advantages to the hollow camshaft design include cutting down on weight and being able to lubricate through the camshaft.
Known from JP 61 115 660 A, JP 41 67 946A, JP63 264 248A and JP 62 296 935 A is to manufacture camshafts out of cast iron in a lost-foam casting procedure.
The object of the invention is to be able to manufacture a generic camshaft out of a high strength material as rationally as possible.
The casting models are designed according to the principle of the lost-foam casting system. This means that the camshaft is generated and used as a lost mold, e.g., consisting of a polymer blank, with a slight outside addition of material for final processing. This blank dissolves when the cast steel is filled in, and is placed in a sand mold, wherein the hollow interior cavity is also filled completely with sand.
The polymer used has a special chemical composition, which prevents the harmful carbonization processes from taking place while pouring in the liquid steel. This satisfies the high geometric requirements placed on the casting mold during the implementation of the instruction according to the invention.
To prevent casting defects and for economic considerations, a special feed system is used according to the invention, making it possible to simultaneously cast numerous camshafts, e.g., more than 50. The plug-in system is used to ensure the stability of a so-called nest of molds comprised of more than 50 camshaft blanks with feed system. Adhesives need not be used here, which reflects favorably on casting quality.